This invention relates to an image reader.
Generally, an image reader for reading an original of paper, etc., placed on a transparent original bed of glass, etc., and outputting image data has been known. The image reader converts light from the original into an electric signal by using a line sensor as image pickup device comprising photoelectric conversion elements such as CCD placed linearly in a main scanning direction. The electric signal output from the line sensor is an analog electric signal and thus is converted into a digital signal by an A/D conversion section. The digital electric signal is subjected to various corrections of gamma correction, shading correction, etc., and then is output to a personal computer, etc., outside the image reader as digital image data.
To read a color image through the image reader, analog electric signals of colors of R, G, and B are input to the A/D conversion section from the line sensor. The input color signals are output from the A/D conversion section as digital electric signals in synchronization with the timing of a clock signal supplied to the A/D conversion section.
For example, to use an image reader with 12-bit output of each color, an A/D conversion section 100 is provided with 12 pins of D0 to D11 as output pins, as shown in FIG. 4. The A/D conversion section 100 and an image data generation section 110 are connected through connection lines 120.
Assume that the D0 to D7 pins output high digital electric signals at the same time as output gradation corresponding to the analog electric signals input to the A/D conversion section 100 at one clock signal. Assume that the D0 to D2 pins output high digital signals and the D3 to D11 pins output low digital signals as output gradation of the A/D conversion section 100 corresponding to the next clock signal.
At this time, the D0 to D2 pins hold the digital electric signals high. In contrast, the D3 to D7 pins make a high to low transition and the D8 to D11 pins hold the digital electric signals low.
By the way, the digital electric signal output from the A/D conversion section 100 is a high frequency. Accordingly, when the output digital electric signal makes a high to low transition or a low to high transition, electromagnetic radiation noise (EMI) occurs from the A/D conversion section 100. Particularly, if the digital electric signals output from the adjacent pins of the A/D conversion section 100, such as D1 and D2 or D2 and D3, make a high to low transition or a low to high transition at the same time in synchronization with the clock signal, a problem of amplifying EMI and increasing noise is involved.
When EMI occurs, it is feared that the digital image data may contain noise and the quality of the image read through the image reader is degraded; this is a problem.
To prevent EMI from occurring, a method of providing an EMI filter, putting a shield on wiring, or the like is possible. However, a member such as the EMI filter or the shield is added, the structure becomes complicated and the space for placing the member needs to be provided and problems of upsizing the image reader and an increase in the cost accompanying the added member are involved.